The invention relates to a method and assembly for producing oil and/or gas through a well traversing stacked oil and/or gas bearing earth formations that are separated by one or more sealing earth layers having a low permeability.
If oil and/or gas is to be produced via a single well that traverses a plurality of stacked oil and/or gas bearing earth formations, that are generally called stacked reservoirs, then the shooting of perforations into these reservoirs and the subsequent installation of sandscreens and production equipment within the well may be a time consuming operation. The fluid pressure of the fluids in the pore spaces of the stacked reservoirs may be different, which may induce fluid to flow via the well from one reservoir to another, which may lead to an uncontrollable flux of fluids from a high pressure to a low pressure reservoir and sand erosion and/or deposition within the still uncompleted wellbore.
Typically perforations are shot into the oil and/or gas bearing formation, the well casing and/or well liner surrounding the wellbore by a perforating gun assembly as known from U.S. Pat. No. 6,404,139 before installation of the sandscreen and well packers in order to prevent damage to these fragile pieces of equipment.
It is known from US patent application US2003/0230406 to arrange perforation guns on a strip arranged in the annulus between a sandscreen and a production tubing such that the guns shoot perforations in a tangential direction into the tubing. This known perforation method involves a significant risk of damage to the sandscreen and only shoots perforations of a limited depth into the formation surrounding the tubing.
It is an object of the present invention to provide a method and assembly for producing oil and/or gas through a well traversing stacked oil and/or gas bearing formations, wherein perforations can be shot in a quick and efficient manner into the surrounding formation, well casing and/or liner and such that after shooting of the perforations flux of fluids between the various oil and/or gas bearing formations can be inhibited.